I'm just putting this together as a little one-stop subjob compendium.

I've seen these put together before, and I find that working by lvl is the cleanest and most useful way to present this information.

So:

SCH Subjob Guide

Lvl 1-11: the solo lvls. Use what you like here. My personal advice is to use /MNK for the added VIT and HP, /PUP for the rather strong pet (with capability to cure), /WHM for the earlier spells, or /SMN for another strong pet (though PUP would be better MP-wise).

Lvl 11-19: Valkurm Dunes.

NOTE: from 11 on I will be sticking to /WHM, /BLM, or /RDM, as these are clearly the subs that benefit SCH the most. Other subs would be more situational than anything. Also, I will list spells that the sub would give earlier than SCH main gets it.

Summary: BLM picks up a few points here, but its been said before: Warp is a terrible reason to pick /BLM as your subjob. Its also important to note that although /RDM's Enthunder is rather insignificant in Garlaige, it (and the other En-spells) become rather nice with the -ga ability SCH gets later on.

Summary: In my opinion, at lvl 40+ /RDM becomes a better sub for nuking than /BLM. It catches up on MAB, but gains gravity, and (if it works that way) has the added benefit of Fast Cast. /WHM is still the hands-down support-role winner though.

Summary: Here it becomes clear: /BLM falls behind as a sub for SCH. /RDM is a very strong sub for the SCH leaning towards nuking (and enhancing: En-spell-gas are a very nice option); /WHM is very strong for the SCH leaning towards healing.

Summary: /BLM has its uses. Lvl 60+ it gives you Magic Attack Bonus II, which is nothing to sneeze at. /RDM gains some interesting enhancing spells, which can be -ga'd with SCH's abilities. /WHM adds its signature Tele-spells, plus more status cures.

All in all, it looks like each of these three subs adds exactly what its main-job purpose is, and rolls it directly into SCH's functionality. I'd say all three subs are fairly strong in the proper situation.

MORE DETAILS:

Conclusion #1--WHM is the strongest sub at lower lvls. It offers the biggest pool of spells to add to SCH's repertoire. It remains a solid sub all the way to 75 though.

SCH's ability to -ga enhancement spells make some of WHM's spells superstars.

Conclusion #2--RDM is the strongest sub in terms of enhancing. It adds several single-/self-target spells that combine terrifically with SCH's -ga ability. RDM is at its strongest as a sub at 40+, when it gives SCH Magic Attack Bonus and SCH gets access to Accession.

I think that with so many DNC out there atm, you're more useful going /RDM or /BLM for +MAB and support healing, but that's just my opinion. Accession still gives you access to Protectra without /WHM as well.

At level 30 /BLM offers Wizard's Earring latent effect of Elemental skill +5. This is badly needed to improve nuking since SCH has only B+ elemental skill, especially if the player does not already have at least 3 elemental merits active at that level.

I agree with the OP's general conclusions about subjobs, but have a lower opinion of /BLM than the OP. MAB II is only +4 MAB. Tier I -gas, Poisonga, Sleepga, Conserve mp, Elemental DOTs, Warp/Escape, and Blaze/Ice spikes are much weaker than what /RDM offers. It works for a low level sub when you're solo, mana/book burning, or acting as a BLM substitute in a party. But really as you reach the 40's /RDM starts pulling ahead with AOE enspells and a full set of enfeebles including Gravity at 42. Its not long after that that you finally start getting some defenses like MDB I, Blink, and later on Stoneskin and Phalanx. /RDM MAB I vs /BLM MAB II is 20 vs 24. You should probably agonize over it in the 20-39 levels, but once /RDM provides it you'll be better off with /RDM. You can AOE your enspells 75% of the time. Hopefully they operate on your enhancing magic skill, not that of the ones doing the meleeing.

And all of this is largely dependent on if a party needs your healing ability in a significant way. Curagas and status fixes will generally outweigh a magical offense as you get past the 40's and into 50+. If a party wants magical damage, a BLM is a better choice than a SCH anyway. SCHs may wind up soloing on Beastmen pets the way BLMs do, but will probably have a hard time of it since they'd have to choose between MAB and enfeebles or /NIN for some defenses. Their nukes aren't going to one shot stuff, and many pets are bats, which don't sleep easily... so even for enfeebles a SCH is stuck with just Bind and Gravity and Blink to protect themselves for a lot of the 50+ BST pet levels. If they /NIN to be survivable, they won't have any enfeebles or MAB. Luckily, SCH/WHM will make pretty solid healers so they should still get some regular invites.

/RDM very good general purpose and solo subjob, gives nice Enhancing magics and full set of enfeebles, MAB and MDB, Dia & Bio I/II, Gravity, Dispel, Fast cast.

/BLM seldom used, gives sleepga, some dark magics and black enfeebles including sleepga, ES, spikes, Conserve MP, Warp/Escape, Elemental DOTs, and MAB II. Problem is no gravity or defenses so not very good for nuke soloing, and dangerous in a group if heavily focused on nuking because of no Blink or Stoneskin. Subjob latent earring +5 elemental skill.

/BLU won't offer any really useful spells, but can get MAB and autoregen, plus some stats like some mp and INT/MND. If you stand close enough you can spam Headbutt, lol. Cocoon's ok. For soling worms at low levels, this gives a weak stoneskin, which can let you rest while Rasped, but you lose Dia or Bio which you need prevent hp their regen while you rest mp, and after lvl 20, lose out on MAB from /BLM. It could work in a mana/book burn vs worms from 12-19 though, where someone else in your group has dia.

Sadly, I'm hearing reports that AOE enspell, phalanx, and Stoneskin all use the recipients' Enhancing Magic (and MND in the case of Stoneskin) to determine the strength of the effect. This means enspells do 1 damage for most melee jobs. /RDM still gives a lot of awesomeness but AOE buffing looks to be pretty weak. Aquaveil, Invisible, Protect, Shell, and Blink all work at full effect. No confirmation on other stuff yet, except that Spikes spells, Reraise, Raise, and Warp don't work at all. Wondering about regens and barspells...

I use /BLM for sub right now, but I have elemental merits to help, I notice I was out nuking a BLM in quifim by 20-50 damage. I have all the subs leveled, so I can switch any time, seeing as what the party needs. But I do not want SCH to turn into another WHM.

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